Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

Second Normal Form (2NF)

  • Marcelo ArenasEmail author
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1263




Let R(A1,…, An) be a relation schema and Σ a set of functional dependencies over R(A1,…, An). An attribute Ai (i ∈{1,…,n}) is a prime attribute if Ai is an element of some key of R(A1,…, An). Then specification (R, Σ) is said to be in second normal form (2NF) if for every nontrivial functional dependency X → A implied by Σ, it holds that A is a prime attribute or X is not a proper subset of any (candidate) key for R [1].

Key Points

In order to avoid update anomalies in database schemas containing functional dependencies, 2NF was introduced by Codd in [1]. This normal form is defined in terms of the notions of prime attribute and key as shown above. For example, given a relation schema R(A, B, C) and a set of functional dependencies Σ = {A → B}, it does not hold that (R(A, B, C), Σ) is in 2NF since B is not a prime attribute and A is a proper subset of the key AC. On the other hand, (S(A, B, C), Γ) is in 2NF if Γ = {A → B, B → C}, since Ais a key (and thus it...

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Recommended Reading

  1. 1.
    Further CEF. Normalization of the data base relational model. In: Data base systems. Englewood Cliffs: Prentice-Hall; 1972. p. 33–64.Google Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Pontifical Catholic University of ChileSantiagoChile

Section editors and affiliations

  • Leonid Libkin
    • 1
  1. 1.School of InformaticsUniversity of EdinburghEdinburghUK